Electrical conductor and process of making the same



Sept. 29, 1936. R. SELQUIST ELECTRICAL CONDUCTOR AND PROCESS OF MAKINGTHE SAME Filed April 8, 1935 INVENTOR Patented Sept. 29, 1936 UNITEDSTATES PATENT OFFICE ELECTRICAL CONDU F MAKIN CTOR AND PROCESS GTHESAMERolf Selquist, McKeesport, Pa.,

per-weld Steel Company,

assignor to Can- Glassport, Pa., a cor- 80laims.

This invention relates to a novel article of manufacture useful as anelectrical conductor which must possess considerable tensile strength.More particularly, the invention relates to a conductor of the type usedfor transmission lines where the spacing of the towers or other supportsis suiilcient to require a conductor whose ultimate strength is high.

Certain cheap metals, of which copper is the 10 most satisfactoryelectrical conducting material,

have relatively high conductivity, and indeed copper is accepted as thestandard among metals in this characteristic. These metals andparticularly copper, however, are subject to the drawll back for use intransmission lines that the relatively low ultimate strength of themetal limits the maximum length to which the spans may be carried. Forincreasing the ultimate strength of such conductors, wires have beenproduced having a a steel core surrounded by a sheath of copper. Thisproduct, in comparison with copper wire having the same conductivity, isconsiderably more expensive 0n the other hand, this bimetallic producthas considerably higher ultimate strength than pure copper. The latterhas an ultimate strength of approximately 60,000 pounds per square inch.A good product of the bimetallic type'iust referred to has an ultimatestrength which is of the order of three times that a of copper. Thus,with this bimetallic product it is possible to increase the length ofspan in electric transmission lines beyond what is possible with a purecopper conductor.

. One object of the present invention is to pro- .35 vide a novelarticle of manufacture which combines the advantageous features of anall copper conductor and the high ultimate strength oi the bimetallicproduct above referred to, particularly in asymmetrical cables composedof wires of 4. widely diiferent physical characteristics.

A further object of my invention is to provide an improved method ofmanufacturing such a product.

drawing which illustrates In the accompanying a my invention.

Fig. 1 is a view in side elevation and Fig. 2 is a view in cross sectionof a two-strand con ductor embodying my invention;

Fig. 3 is a view in side elevation and Fig. 4 is ,a

I view in cross section of a similar article composed of three wires:and

Fig. 5 is a diagrammatic view illustrating the stranding of compositewire for producing such; a conductor.

In accordance with my invention, I combine in a composite electricalconductor a wire of a single metal having high conductivity with abimetallic wire having a core of higher unit strength than the metal ofhigh conductivity and having a sheath of said metal of highconductivity. I 5 strand the composite conductor by laying the wiresagainst each other substantially on the axis of the conductor. I preferto use as the wire of a single metal a copper wire because of its highconductivity; and I prefer to use copper as the sheath of the bimetallicwire, the copper sheath being permanently bonded with the core. Forpurposes of increasing the ultimate strength of the product, the core ofthe bimetallic wire is preferably steel.

My improved article of manufacture is illustrated' by two embodiments,one of which consisting of two wires is shown in Figs. 1 and 2. The wireof a single metal is indicated by the numeral 6 and the bimetallic wireis indicated by the numeral 1. As above set forth, the wire 8 ispreferably a copper wire and the wire I preferably comprises a core C ofa metal of higher unit strength than the copper while the sheath S is ofcopper.

A second. embodiment of my invention is 11- lustrated in Figs. 3 and '4.The composite electrical conductor is made up, in this embodiment, ofcopper wires 9 and I0 and a bimetallic wire ll. Here again, the wire Hpreferably comprises a so core 0 of steel and a sheath S of copperpermanently bonded to the core. With a threewire type of conductor itis, of course, possible to substitute a bimetallic wire for eitherthewire 9 or the wire l0; but such a-conductor has not in general the fieldof usefulness that the embodiments shown have.

There is one respect at least in which the several embodiments of myinvention are a distinct departure from electrical conductors heretofore40 produced. There is a lack of balance of the metal of high unit.strength about the central axis of the conductor. It will be noted thatin Fig. 2 the bimetallic wire on one side of the axis is not balanced bya similar wire on the other side of the axis of the conductor. In thesame way, the bimetallic wire introduces a lack of symmetry into theembodiment shown in Fig. 4. While this introduces into the manufactureof the conductor problems peculiar tosuch asymmetrical 5 distribution ofmetal of high unit strength about the axis of the conductor, I havefound that by modifying the customary practice in stranding the wires,these diiiiculties can be overcome.

In the production of composite conductors of this type the usualstranding practice should be modified to take care of the distinctcharacteristics of the bimetallic wire, including the greater rigidityor stiffness of such wire. It is customary in stranding a compositeconductor to preform the several wires entering into the strand beforethey reach the closing die. It has been discovered that if thiscustomary practice is followed in making my improved product, the wiresdo not lie close together in the strand. This is due to the'fact. thatthe copper wire or wires are more plastic and have less stiffness thanthe bimetallic wire. In overcoming thisdifllculty I accentuate thepreforming action on the bimetallic wire while reducing or almosteliminating the preforming action on the copper wire or wires. 7

As illustrated diagrammatically in Fig. 5, the several wires are asusual unwound from bobbins l4, l5, etc., and passed about guides l1, l8,etc. to the closing die 20, the bobbins and guides being carried on arevolving spider (not shown) in the customary manner.

I have found that if the preforming action on the copper wire by itsrespective guide, in Fig. 5 the guide It, is greatly reduced or almosteliminated, the stranding operation functions smoothly and the wires lieclose together in the finished conductor. Preferably, the guidecooperating with the copper wire is so formed as to eliminate any sharpbending as the wire passes about the guide. These guides are customarilyrollers, and the desired purpose may be accomplished by increasing thediameter of the roller. The preforming action is also controlled to aconsiderable extent by the drag imposed upon the bobbin by the usualbrake indicated at 2|. The bobbin from which the copper wire is unwoundis -allowed to revolve with but slight braking action.

' Accordingly, the copper wire running to the closing die is practicallystraight.

On the other hand, the accentuation of the preforming action on thebimetallic wire may be secured by causing the bimetallic wire to make asharper bend about its respective guide, and

furthermore by increasing the braking action on the bobbin. The resultof the accentuation of the preforming action on the bimetallic wire andthe reduction in the preforming action on the copper wire is to enablethe closing die 20 to closely. and uniformly intertwine the wires into auniform strand.

The term preformed" as it appears in this description of my inventionand in the claims is used in the sense of forming the wire into apermanent helix before it goes into the closing die. The term preformedis not used in the claims with the intent that itshould be construed asthe action of straightening a wire.

The product produced in accordance with my invention has, in addition tothe advantages pointed out in the above description, further advantageswhich are inherent in the product. The moduli of elasticity (Youngsmodulus) of the bimetallic wire and of the copper wire are such that,within the limits of strain to which such conductors would generally besublected in service, the load applied to the conductor is distributedbetween the wires in proportion to the moduli of these wires.Accordingly. the bimetallic wire carries a larger proportion of the loadthan the copper wire or wires, thus utilizing the full strength of allof the component wires without premature over-stressing of eithermaterial. This is in contrast to composite conductors in which the wireshave all the same modulus of elasticity. In such a case, the strainstend to cause equal loading in all of the component wires.

This would result in proportioning the loads, not

according to the strengths of the individual wires, but equally, whichis disadvantageous.

. A further advantage inherent in my improved product is that there isno chemical dissimilarity between the wires exposed to the atmosphere.In other words, there is no tendency to establish electrogalvanic actionor electrolytic deterioration within the cable, such as is apt to occurwhen two dissimilar metals are juxtaposed.

A further advantage lies in the freedom from vibration of the conductorwhen strung on long spans with high stringing tensions. The particularshapes of these conductors are such that they have little or no tendencyto vibrate in winds. As is well known, such vibration is objectionable,as it subjects the conductor to excessive stresses and to chafing atpoints of support.

It is furthermore noteworthy that in accordance with my invention wiresof radically different characteristics, particularly with respect totheir unit strength, are combined into a uniform conductor. It will beapparent that this constitutes a notable contribution in the way of m al possible the production of a conductor having the wires so strandedthat the metal of high unit strength is asymmetrically distributed aboutthe axis of the conductor.

While I have illustrated and described certain preferred embodimentswhich my invention may assume, it will be understood that my inventionmay be otherwise embodied and practiced within the scope of thefollowing claims.

I claim:

1. In the method of stranding a composite cable comprising a wire of asingle metal and a bimetallic wire having a core of higher unit strengththan the metal of the first wire. the steps consisting in preformingthe-bimetallic wire to a considerably greater extent than the wire of asingle metal, and then intertwining the wires and passing them through aclosing die.

2. In the method of stranding a composite cable comprising a wire of asingle metal and a bimetallic wire having a core of higher unit strengththan the metal of the first wire, the steps consisting in accentuatingthe preforming action on the bimetallic wire as compared to that properfor the stranding of a composite cable of similar wires whilesubstantially reducing the preforming action on the wire of a singlemetal, and then intertwining the wires and passing them through aclosing die.

3. A composite electrical conductor comprising a wire of a single metalhaving high conductivity stranded with a bimetallic wire having a coreof higher unit strength than the metal of high conductivity and having asheath permanently bonded thereto of said metal of high conductivity,the bimetallic wire being preformed to lie against the wire of a singlemetal and both wires being disposed in substantially equal helices aboutthe axis of the conductor.

4. A composite electrical conductor composed of wires closed about theaxis of the conductor without a central core wire, the component wirescomprising a preformed bimetallic wire having a core of relatively highunit strength and an integrally united sheath of metal of relativelyhigh conductivity, and a wire of said metal of high conductivity twistedtherewith while in. substan' tially straight condition so as to betwisted to sub stantially conform to the shape of said bimetallic wireone bimetallic wire having a core of relatively high unit strength andan integrally united sheath of copper and stranding it together with atleast one unpreiormed copper wire without a central core wire, andpassing the stranded wires through a closing die.

7. A composite electrical conductor as claimed in claim 3 in which thewire of a single metal is a copper wire and the bimetallic wire has asheath of copper permanently bonded to a core of steel. 8. A compositeelectrical conductor comprising 5 a bimetallic wire having a sheath 01'copper permanently bonded to a core 01' steel and at least one copperwire, said wires being twisted about the axis or the conductor without acentral core wire, the bimetallic wire being formed into permanenthelices before being stranded with the remainder of the wires, and thelatter being in substantially straight condition before they are twistedabout the axis of the conductor so as to be twisted to substantiallyconform to the shape of said bil5 metallic wire.

ROLF SELQUIBT.

